Method to Produce Golden Bronze by Diffusion of Tin Into Copper Under Controlled Conditions

Abstract

The present invention relates to the production of a bronze plated substrate having a golden appearance thanks to a multiple-layer plating method. The method notably comprises plating a substrate having at least one layer of copper with a tin layer which thickness represents 3.5% to 12% of the copper layer thickness. The method further comprises annealing the plated substrate in an annealing furnace comprising a plurality of heating zones, the last heating zone of the furnace having an annealing temperature ranging from 600° C. to 815° C. The annealing step of the method is performed under controlled operating parameters which comprise an annealing residence time, the annealing temperature and the relative thickness of the tin layer in view of the copper layer. The operating parameters are controlled in accordance to each other to ensure obtaining the gold-like appearance of the plated bronze.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the production of bronze objects having a golden appearance. More particularly, the present invention provides a multi-layer plating method to produce a golden bronze alloy layer on substrates, comprising non-cyanide plating of successive metals.BACKGROUND OF THE INVENTION[0002]Bronze is commonly defined as an alloy of copper and tin. However, other metals can be used, defining different bronze alloy variations such as commercial bronze (copper, zinc), architectural bronze (copper, zinc, lead) or aluminum bronze (copper, aluminum, nickel). The color of the bronze depends on the exact composition of the different metals used in the fabrication of the alloy. For instance, a copper-rich bronze alloy may have a reddish appearance whereas a tin-rich bronze alloy may have a silvery-white appearance. The golden appearance of bronze is then the result of a specific metallic composition.[0003]Bronze can be obtained as a solid alloy...

AI Technical Summary

Benefits of technology

The patent describes a method for producing a bright yellow gold colored bronze layer on a plated substrate. This is achieved by gradually diffusing tin layers into the copper layer through a process of annealing at different temperatures. The method prevents the tin from vaporizing or forming puddles on the surface of the plated substrate. The result is a smoother and more uniform surface with improved brightness.

Problems solved by technology

However, cyanide-based plating solutions are very toxic.

This toxicity is long lasting and poses extremely high health and safety risks to humans, live animals and fish far downstream from the source of spills and leaks in case of accidents or negligence in handling the plating solutions.

Disposal of the waste is expensive and dangerous since the chemicals used to destroy cyanides are also toxic by themselves.

Minute amounts of cyanides, in the parts per million range can cause severe damages and can be lethal in some cases to people and animals.

Non-cyanide bronze by the plating process can be obtained by proprietary commercial formulations but the results are usually poor because the plated products come out in a reddish color, resembling very much copper, rather than goldish as one would expect when bronze is desired.

The non-cyanide plating solutions tend to be unstable, expensive and difficult to control for consistent results and color.

This is the reason why non-cyanide bronze plating is not popular and not used, particularly, when plating is done for large quantities of industrial products, such as coinage blanks.

The resulting coins have a regular surface exempted of surface pinholes which is normally an inherent problem of successive metals electroplating followed by annealing diffusion.

However, unlike zinc in brass diffusion, tin does not easily diffuse into the copper matrix because of its low melting point.

Thus, by following the same approach with the combination of copper and tin, golden bronze cannot be produced.

It does not allow the production of commercially suitable golden bronze.

Without being specific and precise, the teaching of that reference is inapplicable and unworkable for a person skilled in the art searching a solution for the production of non-cyanide golden bronze.

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